1. Field of the Invention
The invention relates to a running control device for a watercraft with a device for electrically controlling the amount of intake air to an engine.
2. Description of the Related Art
In conventional watercrafts, a throttle lever manipulable by a user and a throttle valve provided in an intake passage of a propulsion device constituted by an engine, are mechanically connected to each other with a cable or other mechanical elements. A throttle valve opening is determined uniquely by throttle lever operation.
Alternatively, it is possible, as proposed in JP-A-2000-108995, that a throttle controller generates an electrical signal to drive an actuator mounted on a throttle valve so that the relation between throttle lever position and throttle valve opening is set to be non-linear, yet the throttle valve opening is determined uniquely by the throttle lever position.
Control of a watercraft is difficult for a beginner, and it takes a veteran driver to operate the watercraft skillfully. For example, when cruising, during which a watercraft runs at a constant speed, specifically in water-skiing, trolling, or the like, the user (driver) should take notice of engine speed and watercraft velocity at all times and fine-tune the throttle opening continuously.
However, the circumstances surrounding a watercraft are not always constant, and the characteristics of ship control change widely depending on various disturbances. For example, the area of submerged portions of the hull changes with changes in weather or sea conditions, the number of crew, the amount of gear, steering operation or trimming operation, or the like, and running resistance changes accordingly, which causes engine speed or watercraft velocity to change every moment even if throttle opening is constant. Controlling a watercraft during cruising in such circumstances while fine-tuning the throttle opening can be burdensome and thus the driver can be distracted especially if he is a beginner.
In addition, if velocity and throttle opening are ill-balanced during ship control, a phenomenon called cavitation, where the propeller races due to formation of air bubbles, may occur, which raises engine speed abruptly, resulting in damage to the engine, propeller, or other driving systems.
An engine speed control system or a velocity control system can be used for a conventional control device for watercraft cruising.
One benefit of an engine speed control system is that cavitation is quickly suppressed as soon as it happens. However, when the resistance between the hull and the water changes, a driver should change the target engine speed in order to maintain a constant watercraft speed.
A benefit of a watercraft velocity control system is that a watercraft can run at a target speed regardless of the change of the resistance to a hull. However, when cavitation occurs, the thrust is reduced which causes the watercraft to slow. The velocity control system then further opens the throttle to compensate for the reduced watercraft velocity, whereby more cavitation is caused.
While a watercraft is running with an engine speed cruising control system, and if an operation, like turning is performed, which changes the posture of the hull rapidly, the resistance to the hull is increased whereby velocity relative to water is decreased. If a watercraft velocity control system is employed, and the velocity is decreased considerably, a throttle is opened to compensate for the change in watercraft velocity and the probability of the generating cavitation will be increased.
In view of the foregoing, it is an object of the invention to provide a running control device for a watercraft capable of effecting an easy cruising control of the watercraft even by a beginner, especially, allowing stable running while turning, and preventing cavitation.